Keratinised tissues and/or structures, in particular the nail, are prone to a range of diseases, conditions and/or disorders.
Ingrown nails (onychocryptosis) are a common problem that occurs when the nail embeds into the lateral nail groove and resulting in inflammation causing pain and discomfort along the margins of the nail. The main cause of onychocryptosis in toe nails is the wearing of unsuitable footwear that applies excessive side and or top pressures to the nail. Other causes include high levels of foot moisture softening the nail and extending the epidermis keratin which can change the convex arch permanently. Other causes include genetics, accidental trauma, incorrect nail trimming or disease. An alternative school of thought promoted by Vandenbos and Bowers (Can. Fam. Phys. 54 (11): 1561-1562) is that the “Ingrown Toenail” can result from excess skin forming around the nail and that the nail may not be the causative factor, they hypothesize that the soft tissue should be excised rather than the ingrown segment of the nail.
The most common therapy for onychocryptosis is phenolization which uses phenol (known as carbolic acid, hydroxybenzene, monohydroxybenzene, benezenol, C6H5OH) to permanently ablate the part of the nail matrix that makes the section of the ingrown nail. This technique is referred to as partial matrixectomy or phenol avulsion. The treatment using phenol can occasionally result in infection as it is invasive and damages the skin barrier and requires aftercare treatment. In some cases incorrect or inadequate treatment can result in partial regrowth of the nail which leads to recurrence of the condition as the re-growing nail fragment embeds into the nailfold. This requires repeat treatment to ensure that the treatment is effective. Caution must be taken with phenol as excess application has the potential to cause burns to surrounding tissues.
In chronic onychocryptosis cases a full nail removal (avulsion) is sometimes used to treat the problem. In this treatment the nail is removed and the full nail matrix is cauterised using a caustic agent (such as phenol or sodium hydroxide) to prevent the nail regrowing. Again in some instances incorrect or inadequate treatment can result in partial regrowth of the nail requiring repeat treatments to prevent recurrence.
There are a number of other treatments including the Vandenbos procedure where excess tissue around the nail is surgically excised and mechanical intervention treatments that involve correcting the shape of the nail or removing pressure caused by the nail against the nail fold. However these techniques are not widely employed and phenolization remains the treatment of choice.
Phenol is a highly caustic chemical and is also a VOC (Volatile Organic Compound), and phenol vapour is known to be harmful to the eyes, skin, respiratory system digestive system, heart, kidney, liver, lung, peripheral nerves, and the unborn child. Phenol is readily absorbed through the skin or through inhalation and prolonged inhalation of phenol vapour may cause digestive, nervous, skin, liver and kidney problems.
Whilst not classified as a human carcinogen, phenol has also been shown to cause cancer in laboratory animals, and may cause mutagenic effects, as reported by British Data Hazard database (EM Science database) and by Clayton & Clayton L V. Patty's Industrial Hygiene and Toxicology, 3rd Edition, J. Wiley and Sons, New York, 1982. The Health and Safety Executive in the UK reviewed occupational exposure limits for phenol and could no longer identify a safe level, as a result they issued a chemical hazard alert notice for phenol in 2000. As of 2007 a long term work place exposure limit (LTEL, 8 hour reference period) for phenol was established of 2 ppm (8 mg m−3). No short term exposure limit (STEL, 15 min reference period) guideline value has been specified. COSHH regulations state that Phenol must not be used if a safer, alternative substance is available, and minimal quantities must be used and stored in the workplace. In many workplaces user exposure is controlled through the frequent rotation of staff that use phenol.
Although this hazardous chemical is an effective and consistent treatment for onychocryptosis, it requires significant controls for use, storage and disposal.
Alternative treatments employ chemical or caustic agents including, sodium hydroxide, liquid nitrogen, urea and other highly acidic or alkaline compounds. Again these treatments require accurate control of the dosage to prevent excess damage and also require specialised storage and handling procedures for caustic chemicals and hazardous gases.
Other treatments include using energy to ablate the tissue and include using laser and radiofrequency (RF) electrosurgery. These treatments do have limitations. Laser treatment is often reported as having good efficacy however the results are often inconsistent based upon user feedback; additionally the systems are prohibitively expensive for most users. With RF ablation users have reported experiencing some problems including nail regrowth and pain. Overaggressive RF electrocautery to the nail matrix can damage the fascia or periosteum underlying the nail matrix.
One of the limitations of RF ablation is that it requires a current path to be established using a grounding pad (Neutral Plate) to conduct the energy from the tissue. This can often cause problems as poor contact with the grounding pad can limit the energy delivered leading to inconsistent treatments and unreliability and in some cases a poorly contacting grounding pad can cause secondary burns from the exit current.
A more suitable treatment would be one where energy can be deposited in a repeatable and controlled manner to a predetermined depth or having a consistent dosage.